1. Field of the Invention
The present invention relates to a control system in a vehicle configured to rotate a drive wheel by a driving power generated in a driving power source, and a method of controlling the vehicle. Particularly, the present invention relates to a system and a method for determining a condition of a road surface on which the vehicle is driving. Moreover, the present invention relates to a system and a method for evaluating a characteristic of the vehicle.
2. Description of the Related Art
In a motorcycle, an internal combustion engine is typically mounted as a driving power source. A torque generated in the internal combustion engine is transmitted to a drive wheel via a driving power transmission path and the drive wheel transmits the driving power to a road surface, thereby enabling the motorcycle to be propelled. If the driving power transmitted to the drive wheel is beyond a gripping capability of the vehicle, the drive wheel spins. The motorcycle can be propelled even under a state where the drive wheel is spinning a little. When the motorcycle is driving off-road, for example, on a road surface with a low friction coefficient, the drive wheel tends to spin significantly. If the spin of the drive wheel becomes severe, driving of the motorcycle becomes unstable. Under the circumstances, Japanese Laid-Open Patent Application Publication No. 2008-111430 discloses that a driving power transmitted to a drive wheel is reduced when a slip value indicating a degree to which the drive wheel spins is more than a predetermined value, thereby suppressing the drive wheel from spinning.
As described above, when the motorcycle is driving off-road, for example, on the road surface with a low friction coefficient, the drive wheel tends to spin to a greater degree. On the other hand, the driver could permit a little spin when the motorcycle is driving on a road surface with a high friction coefficient. There is a tendency that the driver tries to steer the motorcycle carefully to prevent the drive wheel from spinning or to suppress a degree to which the drive wheel is going to spin when driving on the road surface with a low friction coefficient. Therefore, it is difficult to determine accurately a condition of a road surface on which the motorcycle is driving, merely by referring to a slip value indicating the degree to which the drive wheel spins.
As described above, when the torque generated in the driving power source is in excess and is beyond the gripping capability of the vehicle, the drive wheel starts spinning. If both of the generated torque and the gripping capability can be detected during driving, then it is possible to determine accurately whether or not the drive wheel is spinning. However, to accurately detect the generated torque and the gripping capability during driving by calculation of numeric values, a number of parameters are required and the calculation formulas are complex. For these reasons, actually, it is very difficult to detect the generated torque and the gripping capability.